The University of Iowa
The College of Liberal Arts and Sciences
Department of Computer Science

Programming Languages and Tools:

CS:3210:0001

Lecture/Lab #16

Programming with C++

Destructors, std::vector

Warm up

In your own words, define run-time polymorphism

How do we mark a member function as polymorphic?

How do we override a polymorphic function in a derived class?

Destructors

https://repl.it/@agurtovoy/lab16-destructors

struct car
{
    car() { std::cout << "car constructed\n"; }
    ~car() { std::cout << "car destructed\n"; }
};

int main() {
    car c;
}

Called right before the object is destroyed (e.g. when the object goes out of scope)

The primary purpose is to free the resources that the object may have acquired during its lifetime

The "inverse" of a constructor

Has a predefined name and signature: the name of the class prefixed by a tilde (~); has no return value and takes no parameters

Destructors (cont.)

There is always only one destructor for a given class (i.e. destructor cannot be overloaded)

The body of the destructor is executed right before the object is destroyed.

Data members and base classes are destroyed in reverse order from the order in which they were initialized.

Members of user-defined types are destroyed by running the member’s own destructor (if any).

Data members of the built-in types are left as-is.

Destructors are called when:

Variables are destroyed when they go out of scope.

Members and base objects (if any) of an instance of a user-defined type are destroyed when the object of which they are a part is destroyed.

Temporary objects are destroyed at the end of the full expression in which the temporary was created.

if ( true ) {
    car c;
} // c is destroyed

draw( point(0, 0), point(10, 10) );
// both temporary points are 
// destroyed now

std::vector

https://repl.it/@agurtovoy/lab16-vector

A linear collection of objects, all of which have the same type

Often referred to as a container because it “contains” other objects.

Similar to list in Python / ArrayList in Java

Every object in vector has an associated index, which gives access to that object.

v[0]

v[1]

v[v.size()-1]

...

v.capacity()

v.size()

std::vector operations

#include <vector>

int main() {
    std::vector<int> v;
    assert( v.empty) );
    assert( v.size() == 0 );
    // v[0] = 100; // uh-oh, undefined behavior
    v.push_back( 101 );
    std::cout << v[0] << "\n"; // prints 101
}

v.empty()

v.size()

v.push_back( x )

v[n]

for ( auto e: v ) ...

Returns true if v is empty, false otherwise

Returns number of elements in v

Adds a (copy of) element x to the end of v

Returns a reference to the n-th element in v

Iterates through v's elements in linear order

std::vector vs Python's list

numbers = [ 1, 5, -7, 0, 15, 99 ]
print( 'size:', len( numbers ) )

numbers.append( 110 )
print( 'size:', len( numbers ) )

numbers[0] = -100
for n in numbers:
    print( n )

    std::vector<int> numbers = 
        { 1, 5, -7, 0, 15, 99 };
        
    std::cout << "size: " 
        << numbers.size() << "\n";

    numbers.push_back( 110 );
    std::cout << "size: " 
        << numbers.size() << "\n";

    numbers[0] = -100;
    for ( auto n: numbers )
        std::cout << n << "\n";

Python

C++

Exercise 1

Write a program that asks user for a number N, then asks user to enter N integers, then prints the space-separated sequence of integers to the console

https://repl.it/@agurtovoy/lab16-exercise1

Open the exercise template

Write your code, press Run to test

When you're done, grab your Repl's link and send it as a direct message to me (agurtovoy)

Click on the corresponding option in the "Lab16 exercises" poll in #general